To investigate the observed expansion of MZ B cells in RA patients under JAKi treatment, we turned to an in-vitro model of T-cell-independent B cell activation with CpG via toll-like receptor 9 (TLR9), known to support MZ B cell expansion (Supplementary Figure 2 illustrates B cell activation through CpG). The gene discussed is TLR9; the disease is rheumatoid arthritis.